OBD 100

OBD (on-board diagnosis) means that:

- Emission-related components and systems are monitored by the vehicle whilst driving

- Any malfunctions are recorded and indicated by a warning lamp (MIL)

- This information can be read by a diagnostic tester

A further purpose of OBD is to protect vulnerable components such as catalytic converters.

In these operating instructions, OBD is always used to refer to the standard OBD-2 (OBD II). OBD-2 has been obligatory in the USA for all new vehicles since 1st January 1996. In the EU, OBD-2 was introduced for new vehicles with gasoline engine in January 2001 with the EURO-3 standard and for diesel vehicles in January 2004. EOBD is the abbreviation for European on-board diagnosis based on OBD-2.

The OBD diagnostic system is integrated into the electronic control unit and constantly monitors defined emission-related components in the vehicle. The malfunction indicator light (MIL) informs the driver of OBD faults reported by the electronic control unit.

A minimum of five monitoring systems are provided:

- Emission-related components

- Missing combustion

- Fuel system

- Upstream and downstream Lambda sensors

- Catalytic converter efficiency

- Exhaust gas recirculation

- Secondary air system

The following are permanently monitored:

- Missing combustion

- Fuel system (injection times)

- Circuits for emission-related components

The following are monitored once per drive cycle:

- Lambda sensor function

- Catalytic converter function

Speed, temperature and Lambda sensor values can also be read out by way of the OBD diagnostic socket.

In the EU, OBD-2 was introduced for new vehicles with gasoline engine in January 2001 with the EURO-3 standard and for diesel vehicles in January 2003.

Vehicles manufactured before these dates may however also be provided with OBD.

The OBD diagnostic socket is usually situated in the driver's footwell in the area of the center console or in the glove compartment.

The installation location can also be lookedup in the owner's manual of the vehicle concerned or found in the internet.

The malfunction indicator light must come on briefly when switching on the ignition. The malfunction indicator light must go out at the latest when the engine is started. The MIL status (malfunction indicator light "On" or "Off") is read from the vehicle electronic control unit. If the vehicle has detected an emission-related fault, the status is set to "faulty". It is then no longer possible to pass the exhaust emission test. In such cases the malfunction indicator light is permanently lit to show the driver that the vehicle should be taken to a workshop.

The OBD trouble codes (DTC) are defined in SAE J2012 and ISO 15031-6. Manufacturer-specific trouble codes can be defined by vehicle manufacturers.

A trouble code is a 5-position code made up of a letter and four digits. A distinction is made between standard trouble codes which may occur with all vehicle makes and manufacturer-specific trouble codes specified by vehicle manufacturers for certain vehicle models.

A plain language text outlining the cause of the problem can be assigned to each trouble code.

Further information can be gathered from the guide book, chapter 4 (see downloads).